This invention relates to improvements in window shades comprising a headrail, adapted to be mounted to a window frame or the like, a collapsible and extensible shade member, typically but not necessarily a cellular shade member as shown in among others U.S. Pat. Nos.4,450,027 and 4,603,072, cords for raising and lowering the shade member, and a cord lock for securing the cords with respect to the headrail in order to hold the shade member in any particular position desired.
Conventional shades of this type may be considered for the purposes of the present application to have been manufactured according to one of two particularly pertinent designs. Of course, various other shades are known as well. In a first design, referred to herein as the "European"design, which has been on sale for several years, the cords are fixed to a lower edge of the shade member, extend upwardly to the upper end of the shade member, are guided by guide means in the headrail towards one end thereof and thence along the headrail into a cord lock. In the European design, the body of the cord lock is a molded member comprising two integral cord guides. The first cord guide is a vertical cylindrically-curved surface around which the cords are wrapped, changing their direction from parallel to the headrail to outwardly, perpendicular to the plane of the shade member. A second cylindrical member which is curved about a horizontal axis then directs the cords downwardly. A locking dog mechanism, comprising a first dog member pivoted on a support also formed integrally with the body of the cord lock and a second dog member pivoted on the first dog member, is provided to secure the cord with respect to the cord lock.
The orientation of the pivot point of the dogs with respect to the shade member determines the direction in which the cords are moved by the user to cause the dogs to release or to grip the cords. In the European design, the cords make a 90.degree. turn upon redirection from the headrail to the locking dog assembly, and the dogs are positioned such that the cords are moved in a plane generally perpendicular to the plane of the shade member to control it. This is generally not as desirable as an arrangement in which the cords are moved parallel to the shade member, i.e., side-to-side in front of the shade member.
The design of the European design cord lock also was not "crash-proof" , i.e., if the cords were released abruptly by the user, the dogs did not always grip the cord, so that the shade was permitted to fall to its maximum extent; this can be very damaging.
The design of the European design cord lock also exposed the ends of a rivet on which the first dog member was pivoted to the body of the cord lock. For esthetic reasons this is undesirable, and it was desired to conceal this rivet if possible.
The body of the cord lock of the European design was exposed to view, so that if it were to be color coordinated with the remainder of the shade, its material had to be one which accepted color readily. This prevented use of certain functionally-desirable plastics.
A second comparable design which has also been on sale for some years is referred to herein as the "U.S."design. U.S. Pat. No. 4,660,612 to Anderson shows several versions of this design. In this design, the cords again pass around a first guide surface which is curved about a vertical axis and then downwardly over a second guide surface which is curved about a horizontal axis. The cords receive approximately 90.degree. or 135.degree. of redirection about the first curved guide surface before being directed downwardly over the second curved guide surface. This provides relatively substantial frictional drag on the cord, which can lead to difficulty in its operation.
In the U.S. design, the locking dog mechanism is pivoted on a rivet extending through a shroud which is separately assembled to the basic molded body of the cord lock, in which the first and second guide surfaces are integrally molded. In the Anderson patent, the guide surfaces are provided as part of a separate wear-resistant insert. In either case, the shroud can be readily color matched to the remainder of the shade, while allowing the guide surfaces to be formed of a mechanically preferred material. However, the dogs are not located as precisely with respect to the guide surfaces as they would be if their support were molded integrally therewith, as in the European design. Further, the U.S. design also allows the user to see the rivet about which the locking dog mechanism is pivoted, which is generally undesirable, as mentioned above.
The U.S. design is crash-proof, meaning that if the cords are simply released the dogs will grip the cords and prevent the blind from crashing to its maximum extent. On the other hand, the disposition of the dogs with respect to the bearing surfaces is such that the cords at all times are under tension urging them against the dogs; excessive cord wear can result if a rough surface is provided on either of the dogs. This necessitates that the dogs be deburred in the assembly process, which adds somewhat to the cost of the shade.
Thus, both the U.S. and the European designs, while successful commercially, still offer some room for improvement. In particular, the designs of both these cord locks occasionally cause the cords to twist about one another and become tangled.